Love
might be a drug, but humor and laughter have much more
scientifically plausible — and some might say pleasurable
— rewarding qualities, say researchers at the School of
Medicine and Lucile Packard Children’s Hospital.

Using comic strips with and without the punch lines, the
investigators traced the pleasurable aftermath of "funniness" to a
region of the brain involved in the response to methamphetamines
and cocaine, as well as monetary gains and the site of attractive
faces.

In
their study, researchers monitored brain activity in a group of
volunteers while showing them a series of cartoons. Some of the
cartoons had key elements removed to diminish their funniness.
Illustration:Courtesy of
Allan Reiss

"This is the first time that the reward system of the brain has
been linked to humor," said Allan Reiss, MD. "The finding is
potentially significant in terms of understanding normal variation
in personality and behavior as well as certain brain disorders such
as depression." The research was published in the Dec. 4 issue of
Neuron. Reiss is the director of the Stanford Psychiatry
Neuroimaging Laboratory and co-director of the Center for Brain and
Behavior at Packard Children’s Hospital.

Although previous research had identified the regions of the
brain involved in understanding the language and meaning of a joke,
and those required to move the muscles necessary to smile or
chortle in appreciation, no one knew until now why humor feels so
good to most people. This understanding could lead to new
diagnostic tests and therapies for a variety of psychiatric
disorders.

"You
don’t need an imaging study to show that some people use
humor as a very effective coping or stress-reduction mechanism
while others do not," said Reiss, who is also professor of
psychiatry at the School of Medicine and chief of child and
adolescent psychiatry at Packard Children’s Hospital.
"It’s possible that people who rely less on humor simply find
it less rewarding. We’re trying to understand this personal
variation and how it relates to basic behavior and brain
function."

In
the study, 16 young adults were plied with 84 black-and- white
cartoons. As the participants viewed each cartoon, the researchers
simultaneously monitored blood flow in several regions of their
brains using a technique called functional magnetic resonance
imaging. After the imaging session, the subjects rated the "funny
factor" of the cartoons they had viewed in the machine.

The
researchers polled family, friends and students to develop a
portfolio of cartoons to minimize gender or cultural biases that
may have affected the results. They then created an unfunny version
of half of the cartoons to use as controls by removing essential
visual or written cues.

"The
pre-screening of the cartoons were some of the funniest lab
meetings we’ve had," said Reiss. "What’s brilliant
about some of these cartoonists is how perfectly they juxtapose the
line drawing with the caption or a subtle visual perspective. If
you change either one, the cartoon becomes completely
unfunny."

The
researchers found that the giggle-inducing cartoons activated a
network of regions of the brain, including an area called the
nucleus accumbens, or the NAcc, and another called the amygdala. In
the NAcc, which is known to be involved in the rewarding feelings
that follow monetary gain or the use of some addictive drugs, the
degree of activity correlated with how funny the subject thought
the cartoon was; extremely funny clips resulted in more blood flow
to the area than less funny competitors, confirming the
NAcc’s role in humor appreciation.

The
amygdala’s involvement is also telling. Dysfunction in this
region of the brain has been implicated in some pathological
disorders, as well as in depression, and other diseases including
Parkinson’s and fragile-X syndrome, a disorder often marked
by symptoms similar to attention deficit disorder and
autism.

The
involvement of a reward center that responds to addictive drugs
elicits an obvious question: Can humor itself be addictive? In
other words, can inappropriate fits of irrepressible giggles be
blamed on a brain-signaling blip rather than a heartless disregard
of societal expectations? While the idea of biological absolution
is tempting, Reiss isn’t convinced.

"Although it may be involved in addiction, the brain’s
reward center has evolved to enhance learning and behavior through
positive feedback," said Reiss. "It’s meant to allow people
to learn from and perform in their environment in as optimal a way
as possible."

More
important than identifying the existence of hypothetical humor
junkies, the scientists’ finding may one day allow better
diagnostic testing for a variety of conditions.

"One
of the key symptoms of depression is lack of a sense of reward from
previously rewarding activities," said Reiss. "Assessing how the
brain’s reward center responds to humor may turn out to be
the simplest and most direct way to identify people suffering from
mood disorders. I think the applications of this work range from a
better understanding of basic behavior and social interactions all
the way to important clinical issues."